The present invention relates to writing servo track information on magnetic disc drives, and more specifically to propagating servo tracks using an actuator assembly with substantially identical data transducers.
Disc drives are among the most common means of storing electronic information in use today. Ordinary disc drives are typically constructed with the following internal components: one or more magnetic media discs attached to a spindle; a spindle motor that rotates the spindle and the attached discs at a constant high speed; an actuator assembly, located adjacent to the discs, with a plurality of actuator arms that extend over the discs, each with one or more flexures extending from the end of each actuator arm, and with a transducer head (also referred to as a xe2x80x9chead,xe2x80x9d xe2x80x9cread/write head,xe2x80x9d or xe2x80x9csliderxe2x80x9d) mounted at the distal end of each flexure; and a servo positioner that rotates the actuator assembly about a bearing shaft assembly positioned adjacent to the discs such that the transducer heads radially traverse the disc surface (i.e. move back and forth the between the inner and outer diameters of the disc).
Information is stored on and retrieved from a magnetizable material on the disc""s surface. Typically, both the top and bottom surfaces of each disc are utilized to store and retrieve information. Information is transferred to and from a disc surface by a transducer head attached to a flexure at the end of the actuator arm. Each transducer head normally includes an air-bearing slider that enables the transducer to fly on a cushion of air in close proximity to the corresponding surface of the associated disc. Most transducers have a write transducer element and a read transducer element. The write element is used to store information to the disc, whereas the read element is used to retrieve information from the disc.
To facilitate information storage and retrieval, discs are radially divided in concentric circles known as xe2x80x9cservo tracksxe2x80x9d or xe2x80x9ctracks.xe2x80x9d The tracks are given a track number so that the servo positioner can locate a specific track. The servo positioner, upon receiving a control command, aligns the transducer head over the desired track. Information can be stored or retrieved from the disc once the transducer head is in the correct position. The process of switching between different tracks is called xe2x80x9cseeking,xe2x80x9d whereas remaining over a single track while information is stored or retrieved is called xe2x80x9cfollowing.xe2x80x9d
Each track is subdivided into pie-shaped sections called xe2x80x9csegmentsxe2x80x9d or xe2x80x9csectors.xe2x80x9d The two most common types of sectors are informational data sectors and servo data sectors. In a typical disc drive, the informational data sectors usually contain information generated or stored by the user such as programs files, application files, or database files. There may be as few as ten or as many as thousands of informational data sectors dispersed around a single track.
The servo data sectors, on the other hand, contain information that is used by the servo positioner to determine the radial position of the head relative to the disc surface and relative to the track center. Servo sectors typically consist of a Grey code field which provides coarse position information, such as the track and cylinder number, and a servo burst field which provides fine position information, such as the relative position of the transducer head to the track center. Generally the burst fields are used to create a positive voltage on one side of the track centerline and a negative voltage on the other side of the track centerline. A read element on the transducer head can be aligned directly over the centerline by positioning the read element such that the sum of the burst field voltages equal zero.
Servo sectors are usually placed between adjacent informational data sectors on the same track. A clock signal mechanism is used to insure that data intended to be stored in a servo sector does not overwrite data in an information sector (and vice versa).
The number of tracks located within a specific area of the disc is called the xe2x80x9ctrack density.xe2x80x9d The greater the number of tracks per area, the greater the track density. The track density may vary as the disc is radially traversed. Disc manufacturers attempt to increase track density in order to place more information on a constant size disc. Track density may be increased by either decreasing the track width or by decreasing the spacing between adjacent tracks.
An increase in track density necessitates increased positioning accuracy of the read/write transducer elements in order to prevent data from being read from or written to the wrong track. Manufacturers attempt to position the read/write transducer elements directly over the center of the desired track (sometimes referred to as the xe2x80x9cnull error positionxe2x80x9d) when a read/write operation occurs to insure that the information is being read from and written to the correct track. Closely following the track center position at high track densities requires that the tracks be as close to perfectly circular as possible when written to the disc surface.
Tracks are usually written on the disc during manufacturing using one of two means: 1) a servowriting machine, or 2) self-propagated servo writing. In both methods, a timing clock is used to notify the servo positioner when the transducer is over an area where a servo sector is to be written. A write enable signal is activated and servo information is written when the timing pulse indicates that the head is located over a servo sector. The write enable signal is de-activated and information is not written once the head exits the area where a servo sector is to be written.
A servowriting machine is a piece of external equipment that writes servo tracks on a disc drive. The servowriting machine uses a relatively large, very accurate and relatively expensive positioning system which connects to the actuator assembly within the disc drive to precisely align a write element in the drive. The write element is aligned to where the desired track is to be written on the disc surface. A track is written on the disc once the write transducer element is correctly aligned. The servowriter positioning system then moves the write element a predetermined distance to the next desired track location. The servowriter positioning system, therefore, controls both the track placement and track-to-track spacing. There may be several actuator arms with several heads and several write elements attached which will write several tracks at each track location. In this case each track would be written on one side of each of several discs thereby writing a group of tracks or a cylinder of tracks at one time.
Utilizing a conventional servowriter for writing servo tracks has several drawbacks. First, a typical disc may contain tens or hundreds of thousands of servo tracks. The process of aligning and writing each track on the disc is very time consuming and expensive. Second, although very accurate at lower track densities, the servowriter cannot meet the accuracy requirements dictated by ever increasing track densities. Finally, the servowriting procedure must be completed in a clean room because internal disc drive components are exposed during servowriting, again adding expense to the procedure.
A second means of writing tracks on a disc is called self-propagating servo writing. Oliver et al first described this method of servo track writing in U.S. Pat. No. 4,414,589. Several other patents have disclosed slight variations in the Oliver patent, but the same basic approach is used. Under the basic method, the drive""s actuator arm is positioned at one of its mechanical travel range limit stops. A first reference track is written with the write transducer element. The first reference track is then read with the read transducer element as the transducer is radially displaced from the first reference track. When a distance is reached such that the read element senses a predetermined percentage of the first reference track""s amplitude, a second reference track is written. The predetermined percentage is called the xe2x80x9creduction number.xe2x80x9d For example, the read element senses 100% of the first reference track""s amplitude when the read element is directly over the first reference track. If the reduction number is 40%, the transducer is radially displaced from the first reference track until the read element senses only 40% of the first reference track""s amplitude. A second reference pattern is written to the disc once the read element senses the 40% amplitude. The transducer is then displaced in the same direction until the read element senses 40% of the second reference track""s amplitude. A third reference track is then written and the process continues. The process ends when the actuator arm""s second limit stop is reached and the entire disc surface is filled with reference tracks. The average track density is then calculated using the number of tracks written and the length of travel of the transducer.
If the average track density is too high, the disc is erased, the reduction number is lowered so that a larger displacement occurs between tracks, and the process is repeated. If the track density is too low, the disc is erased, the reduction number is increased so that a smaller displacement occurs between tracks, and the process is repeated. If the track density is within the desired range, the reduction number for the desired average track density has been determined, the disc is erased, and servo tracks are written to the disc by alternatively writing servo and reference tracks. The servo tracks are further divided by alternatively writing servo and informational sectors.
Some self-propagating servo writing processes require the read transducer element to be radially offset from the write transducer element so that the read element can sense a reference track""s amplitude without the write element overwriting the reference track. Moreover, the servo tracks must be propagated in the direction of the reader-to-writer offset since the read element must always read previously written servo tracks. In other words, the read element always follows the write element. As a result, current methods of self-propagating servo writing require using different top-surface transducers and bottom-surface transducers since each disc surface requires a read element which follows the write element.
Manufacturing two sets of transducer heads (a top-surface transducer and a bottom-surface transducer) generally complicates the disc drive production process and increases disc drive costs. Each transducer head set must be constructed separately using its own series of masks and redicals during fabrication. In addition, each transducer head set requires its own test platform and may yield different quantities of passing transducers. Thus, maintaining separate lots of top and bottom transducer heads adds expense to the disc drive manufacturing process.
In accordance with the present invention, the above and other problems are solved by providing a structure adapted to use substantially identical transducer heads in upward-facing and downward-facing positions. In this manner, only one type of transducer head need be fabricated, tested, and assembled for disc drives employing self-propagating servo writing. xe2x80x9cSubstantially identicalxe2x80x9d heads, as used herein, refer to those with magnetic field force or sense properties and electrically operative contacts in the same nominal location as one another. More particularly, a head is not xe2x80x9csubstantially identicalxe2x80x9d with its mirror image unless it is bilaterally symmetric.
The present invention generally involves a data storage device comprising a data storage disc having a first disc surface and second disc surface. The data storage device also includes an actuator assembly configured to selectively position a first transducer over the first disc surface and a second transducer over the second disc surface.
In a preferred embodiment, an actuator assembly exchanges data from and to a data storage disc, with the data storage disc having an inner diameter, a first disc surface and a second disc surface. The actuator assembly comprises a first transducer coupled with the actuator assembly. A first read element is mounted on the first transducer, with the first read element configured to read data from the first disc surface. A first write element is also mounted on the first transducer, with the first write element configured to write data to the first disc surface. In addition, the first read element is offset from the first write element by at least the width of one servo track, and the first read element is positioned closer to the inner diameter than the first write element when the first transducer is over the first disc surface. The actuator assembly further includes a second transducer coupled with the actuator assembly. A second read element is mounted on the second transducer, with the second read element configured to read data from the second disc surface. A second write element is also mounted on the second transducer and is configured to write data to the second disc surface. The second read element is offset from the second write element by at least the width of one servo track. Furthermore, the second write element is positioned closer to the inner diameter than the second read element when the second transducer is over the second disc surface.
Yet another embodiment of the invention includes a method for writing servo tracks on a data storage disc having a first surface and a second surface, wherein the first surface and the second surface are bounded by an inner diameter and an outer diameter. The method includes a propagating operation for propagating a first servo seed track pattern radially along the first disc surface from a first start position to a first end position in a first direction. Another propagating operation for propagating a second servo seed track pattern along the second disc surface from a second start position to a second end position in a second direction opposite to the first direction is then performed.
In another embodiment, the present invention optionally includes a disc drive including a data disc with a first disc surface and a second disc surface, where the data disc has at least one servo seed track pattern. The disc drive further includes means for propagating the servo seed track pattern along the first disc surface in a first direction and propagating the servo seed track pattern along the second disc surface in a second direction opposite the first direction.
These and various other features as well as advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.